Optical recording medium recorded with information in depth direction, and method and apparatus of reproduction therefrom

ABSTRACT

An optical disk has a lead-in region provided at the inner circumference side and a user region provided at the outer circumference side. Pit string  3  of pits of different depths-is-formed-in-the-lead-in-region. Light beam reflected from the pit string is detected by detector and TPP and RF signals are output by differential amplifier and addition amplifier. A ternary signal is restored from pits based on the TPP and RF signals. Information is recorded by pits of the same depth in the user region. Recording information in the depth direction in the lead-in region increases the recording capacity thereof The information recorded in the depth direction in the lead-in region cannot be transferred to a user region of another optical disk.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical recording medium in whichinformation is recorded in the direction of depth of the substrate, anda method and apparatus of reproducing information therefrom. Moreparticularly, the present invention relates to a read only or recordableoptical recording medium including a first region in which firstinformation such as additional information is recorded at least in thedepth direction of the substrate and a second region in which secondinformation such as main information is recorded or can be recorded inthe plane direction of the substrate, and a reproduction method andreproduction apparatus of such an optical recording medium.

2. Description of the Background Art

In a conventional optical recording medium such as an optical disk,binary recording is carried out, wherein information is binarized andrecorded corresponding to the presence/absence, the length, the width,or the position in the substrate plane of pits, marks and the like. Morespecifically, pits are provided on the substrate in a read only opticaldisk (referred to as ROM disk hereinafter) to have information recorded.In contrast, recording marks are provided at the recording layer on thesubstrate in a recordable disk such as a phase change disk,magneto-optical disk, and organic dye disk to have information recorded.

Information is transposed to the absence/presence, the length, thewidth, or the position in-the substrate plane of pits, marks or the liketo be recorded on an optical disk. In other words, information isrecorded in the dimension of the plane direction of the substrate usingpits, marks and the like. The string of pits, marks, or the like isarranged concentrically or spirally on a circular substrate to form atrack. The light beam for reproduction follows this track to scan thestring of pits, marks or the like. Taking advantage of the change in thequantity of reflected light, rotation of the plane of polarization oflight and the like based on these pits and marks, recorded informationis reproduced.

The pit string, mark string and the like formed concentrically orspirally are generally assigned an address sequentially from the innercircumference towards the outer circumference. A predetermined region atthe inner circumference side with the smaller address constitutes theregion generally called “lead-in”. Information unique to the relevantoptical disk is written in this lead-in region. More specifically,various information required for the disk drive, disk player, diskrecorder or the like to record information or reproduce informationto/from the optical disk is written in the lead-in region.

Information unique to the disk includes, for example, informationidentifying the disk type (ROM disk, R disk, RW disk, RAM disk, or thelike), information specifying the rotation speed and linear velocity ofthe disk for recording and reproduction, the laser power duringrecording or the like, the address information of a region on the diskthat can be used by the user, key information required to cancel thescramble or encryption, and the like.

The key required to descramble or decrypt is the key used in scramblingor encrypting the contents. The scramble or encryption cannot becanceled without this key. In other words, this release key isindispensable to reproduce the scrambled or encrypted contents.

In accordance with the higher density and higher level of functions ofdisks, the trend is to increase the amount of information written in thelead-in region.

A conventional optical recording medium and a reproduction method andapparatus of an optical recording medium will be described hereinafterwith reference to the drawings.

FIGS. 6-8 show a first example of a conventional optical recordingmedium. FIG. 6 schematically shows the arrangement of pits formed on aROM disk as an example of an optical recording medium. A pit string 33of a plurality of pits 32 are formed spirally on the plane of asubstrate 31, whereby information is recorded.

FIG. 7A is a schematic representation of pit string 33 formed spirallyin the conventional ROM disk of FIG. 6, illustrated in a linear versionfrom the inner circumference region to the outer circumference region ofsubstrate 31. The lead-in region is provided at the inner circumferenceside of the disk, and the user region is provided at its outercircumference side.

The ROM disk ID (identification information), the address information ofthe user region and the like are recorded in the lead-in region. Whenthe information written in the user region is scrambled or encrypted, ascramble key or encryption key thereof is also recorded in this lead-inregion.

Main information such as video and audio data is recorded in the userregion. When the contents become the subject of copyright protection,the main information will be recorded in a scrambled or encryptedmanner.

FIG. 7B is a schematic sectional representation of substrate 31corresponding to pit string 33 of FIG. 7A. The portion of pit 32 isrepresented as a hole. Pit 32 is formed with a constant depth.

FIG. 7C shows an RF signal representing the quantity of reflected lightobtained by reproducing pit string 33 with a reproduction light beam(not shown). FIG. 7D represents a tangential push-pull signal (TPPsignal) obtained by reproducing pit string 33.

The RF signal and TPP signal will be described hereinafter withreference to FIGS. 7C, 7D and FIGS. 8A and 8B. FIG. 8A schematicallyshows the scanning manner of a beam spot 34 of the light beam forreproduction on pit 32. FIG. 8B schematically shows the manner ofreflected light 35 of the reproduction light beam from the disk planeentering photoreceptor elements 36 a and 36 b forming a detector 37 thatis divided into two regions, region A and region B. The RF signal andTPP signal are obtained by the following equations using respectiveoutputs A and B of photoreceptor elements 36 a and 36 b.RF=A+BTPP=A−B

An RF signal having a waveform as shown in FIG. 7C is obtained since thequantity of reflected light of the light beam is small at the pitportion and large at the non-pit portion. Also, since the pit is formedwith a constant depth, a TPP signal as shown in FIG. 7D that changeswith the same polarity will be obtained with respect to all pits, aswill be described afterwards.

FIGS. 11A and 11B schematically show a structure of a string of marks ina recordable disk which is a second example of a conventional opticalrecording medium. FIGS. 11C and 11D represent the waveforms ofrespective signals obtained by reproducing information from therecordable disk.

FIG. 11A schematically shows a mark string 46 formed of a number ofmarks 45 written on the plane of a recordable disk, illustrated in alinear version from the inner circumference region to the outercircumference region of a substrate 41. A guide groove of the light beamthat is generally referred to as a groove is provided in the recordabledisk. The light beam for recording follows this groove 44 or the landwhich is a region between grooves to write a mark 45. Mark 45 can bewritten in either or both of the groove and land. FIG. 11A shows anexample of marks 45 written in groove 44.

FIG. 11B schematically shows a cross section of the disk, correspondingto mark string 46 of FIG. 11A. It is appreciated from FIG. 11B that themark portion is provided so that the reflectance of light differsbetween a mark portion 45 and a non-mark portion 48 in a recording layer47 provided on substrate 41, and not formed as a hole such as for thepit.

FIG. 11C shows an RF signal representing the quantity of reflected lightobtained by reproducing mark string 46 with a reproduction light beam.The quantity of reflected light is smaller in mark portion 45 than innon-mark portion 48.

FIG. 11D represents a TPP signal obtained by reproducing mark string 46.Since mark 45 is formed with a constant depth in groove 44, a TPP signalthat changes with the same polarity is obtained from all marks 45.

FIGS. 12 and 13A-13D show a third example of a conventional opticalrecording medium. FIG. 12 schematically shows a recordable disk thatemploys a phase change recording layer in an unrecorded status as anexample of an optical recording medium. A groove 54 which is a guidegroove is formed spirally on the plane of a substrate 51. Information isrecorded in the form of marks in groove 54. Pits 52 are formed insteadof groove 54 at the inner circumference side of the disk. Informationthat should not be rewritten is recorded by pits 52.

FIGS. 13A and 13B schematically show the structure of a mark string andpit string of the recordable disk of FIG. 12. FIGS. 13C and 13Drepresent the waveforms of respective signals obtained by reproducingrecorded information from the recordable disk.

FIG. 13A schematically shows a mark string 56 formed of marks 55recorded on a spiral groove 54 and a pit string 53 formed of pits 52 inthe recordable disk, illustrated in a linear version from the innercircumference region to the outer circumference region of substrate 51.It is to be particularly noted that marks 53 and pits 52 are aligned inthe lead-in region.

Mark 55 can be written in either or both of the groove and land. In theexample of FIG. 13A, marks 55 are written in groove 54. The lead-inregion is provided at the inner circumference side of the disk, and theuser region is provided at its outer circumference side. In the lead-inregion, recorded are the disk ID (identification information), theaddress information of the user region, and the scramble key orencryption key in the case where the information written in the userregion is scrambled or encrypted.

The user region is recorded with main information such as video andaudio data. When the contents are copyrighted, the main information isrecorded in a scrambled or encrypted manner.

FIG. 13B schematically shows the cross section of the disk correspondingto mark string 56 and pit string 53 of FIG. 13A. Pit 52 is formed as ahole with a constant depth. In contrast to the formation of a hole asfor pit 52, mark 55 is provided so that the reflectance of light differsbetween a mark portion 55 and a non-mark portion 58 in a recording layer57 provided on substrate 51.

Although the depths of groove 54 and pit 52 may be identical, it ispreferable for a shallower groove 54 for the purpose of improving thesignal quality of mark 55. If the signal quality of pit 52 is to be setmore favorable, a depth of approximately λ/4n is preferable, as will bedescribed afterwards. Therefore, it is preferable to form the pit deeperthan the groove. Here, λ is the wavelength of light, and n is therefractive index of the disk substrate.

FIG. 13C shows an RF signal representing the quantity of reflected lightobtained by reproducing mark string 56 and pit string 53 with areproduction light beam. FIG. 13C corresponds to the case where thereflectance of mark portion 55 is smaller than the reflectance ofnon-mark portion 58.

FIG. 13D represents a TPP signal obtained by reproducing mark string 56and pit string 53. Since mark 55 in groove 54 as well as pit 52 areformed with the same constant depth, a TPP signal that changes with thesame polarity can be obtained from any mark and pit.

In the present third conventional example, the relationship between pit52 and the beam spot is similar to that of the first conventionalexample shown in FIGS. 8A and 8B. Therefore, the RF signal and TPPsignal are obtained by the following equations using respective outputsA and B of photoreceptor elements 36 a and 36 b of detector 37.RF=A+BTPP=A−B

An RF signal as shown in FIG. 13C is obtained since the quantity ofreflected light of the light beam is small at the pit portion and largeat the non-pit portion whereas the reflectance is small at the markportion and large at the non-mark portion. Referring to FIG. 13D, a TPPsignal that changes at the same polarity from any pit can be obtained aswill be described afterwards since pits 52 are formed with the constantdepth. The TPP signal obtained from the mark portion and the TPP signalobtained from the pit portion have the same polarity.

In the above-described conventional ROM disk, a greater capacity (largerregion) is required for the lead-in region as the amount of informationwritten in the lead-in region increases. There was a problem that theregion where user data can be recorded on the disk is reduced. Similarlyin the above-described conventional recordable disk, a greater capacitylarger region) is required for the lead-in region as the amount ofinformation written in the lead-in region increases. There was a problemthat the region where the user can write data on the disk is reduced.

From the standpoint of copyright protection, it is not desirable for theinformation in a ROM disk recorded with copyrighted contents to beeasily copied to another recordable disk. However, since theconventional ROM disk has information recorded in the dimension of theplane direction of the substrate using pits, it is theoreticallypossible to copy the information in a ROM disk to another recordabledisk. The role of copyright protection is low. Similarly in aconventional recordable disk, information in the recordable disk can beeasily copied to another recordable disk in theory since information isrecorded in the dimension of the plane direction of the substrate usingpits, marks, and the like. The role of copyright protection is low.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical recordingmedium and a reproduction method and apparatus thereof that allows thecapacity of the lead-in region to be increased while reservingsufficient region for usage by a user without enlarging the lead-inregion.

Another object of the present invention is to provide an opticalrecording medium and a reproduction method and apparatus thereof thatcan prevent copying of a read only disk or recordable disk that isrecorded with copyrighted contents.

According to an aspect of the present invention, an optical recordingmedium recorded with information on a substrate includes a first regionhaving first information recorded at least in a depth direction of aplane direction and depth direction of the substrate, and a secondregion having second information recorded in the plane direction of thesubstrate.

According to the present invention, more information can be recorded inthe first region since the recording density can be increased in thefirst region where information is recorded in the depth direction ascompared with a convention optical recording medium.

Since the first information in the first region is recorded in the depthdirection, copying to another recordable medium that records informationin the plane direction can be prevented.

According to another aspect of the present invention, a reproductionmethod of an optical recording medium recorded with information on asubstrate is provided. The optical recording medium includes a firstregion having first information recorded at least in the depth directionof the substrate by pits of at least two different depths formed on thesubstrate, and a second region having second information recorded in aplane direction of the substrate by at least one of thepresence/absence, the length, the width and the position of a pit formedon the substrate. The reproduction method of an optical recording mediumincludes the steps of reproducing the first information in the firstregion based on a polarity of a tangential push-pull signal obtainedfrom the pits, the polarity differing according to the depth of a pit,and reproducing the second information in the second region based on asignal representing a quantity of reflected light obtained from the pit.

Since the first information is reproduced based on a tangentialpush-pull signal in the present invention, multivalued information cannow be reproduced that was not possible by the conventional reproductionmethod that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light in the second region, a conventional reproductioncircuit can be used for the reproduction circuit of this region.Accordingly, the cost of the reproduction apparatus can be reduced.

According to a further aspect of the present invention, a reproductionmethod of a optical recording medium recorded with information on asubstrate is provided. The optical recording medium includes a firstregion having first information recorded at least in a depth directionof the substrate by pits of at least two different depths formed on thesubstrate, and a second region having second information recorded in aplane direction of the substrate by at least one of thepresence/absence, the length, the width and the position of a pit formedon the substrate. The reproduction method of an optical recording mediumincludes the steps of reproducing the first information in the firstregion based on a signal representing a quantity of reflected lightobtained from the pit and a polarity of a tangential push-pull signalobtained from the pits, the polarity differing according to the depth ofa pit, and reproducing second information in the second region based onthe signal representing the quantity of reflected light obtained fromthe pit.

Since the first information is reproduced based on a signal representingthe quantity of reflected light obtained from a pit and a tangentialpush-pull signal in the present invention, multivalued information cannow be reproduced that was not possible by the conventional reproductionmethod that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light in the second region, a conventionalreproduction-circuit can be used for the reproduction circuit of thisregion. Accordingly, the cost of the reproduction apparatus can bereduced.

According to still another aspect of the present invention, areproduction apparatus of an optical recording medium recorded withinformation on a substrate is provided. The optical recording mediumincludes a first region having first information recorded at least in adepth direction of the substrate by pits of at least two differentdepths formed on the substrate, and a second region having secondinformation recorded in a plane direction of the substrate by at leastone of the presence/absence, the length, the width and the position of apit formed on the substrate. The reproduction apparatus of the opticalrecording medium includes a circuit reproducing the first information inthe first region based on a polarity of a tangential push-pull signalobtained from the pits, the polarity differing according to the depth ofa pit, and a circuit reproducing the second information in the secondregion based on a signal representing the quantity of reflected lightobtained from the pit.

Since the first information is reproduced based on a tangentialpush-pull signal in the present invention, multivalued information cannow be reproduced that was not possible by the conventional reproductionapparatus that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light in the second region, a conventional reproductioncircuit can be used for the reproduction circuit of this region.Accordingly, the cost of the reproduction apparatus can be reduced.

According to a still further aspect of the present invention, areproduction apparatus of an optical recording medium recorded withinformation on a substrate is provided. The optical recording mediumincludes a first region having first information recorded in at least ina depth direction of the substrate by pits of at least two differentdepths formed on the substrate, and a second region having secondinformation recorded in a plane direction of the substrate by at leastone of the presence/absence, the length, the width and the position of apit formed on the substrate. The reproduction apparatus of the opticalrecording medium includes a circuit reproducing the first information inthe first region based on a signal representing a quantity of reflectedlight obtained from the pit, and a polarity of a tangential push-pullsignal obtained from the pits, the polarity differing according to thedepth of a pit, and a circuit reproducing the second information in thesecond region based on the signal representing the quantity of reflectedlight obtained from the pit.

Since the first information is reproduced based on a signal representingthe quantity of reflected light obtained from a pit and a tangentialpush-pull signal in the present invention, multivalued information cannow be reproduced that was not possible by the conventional reproductionapparatus that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light in the second region, a conventional reproductioncircuit can be used for the reproduction circuit of this region.Accordingly, the cost of the reproduction apparatus can be reduced.

According to yet a further aspect of the present invention, a recordedinformation identification method of an optical recording mediumrecorded with information on a substrate is provided. The opticalrecording medium includes a region in which the presence of pits of atleast two different depths formed on the substrate indicatesidentification information that is unique to the optical recordingmedium. The recorded information identification method includes thesteps of detecting a polarity of a tangential push-pull signal obtainedfrom the pits, the polarity differing according to the depth of a pit,and identifying the unique identification information based on thedetected polarity.

In an optical recording medium in which the presence of pits ofdifferent depths indicates identification information that is unique tothat optical recording medium of the present invention, the opticalrecording medium is identified based on the polarity of the tangentialpush-pull signal obtained from the pits. Therefore, the opticalrecording medium can be identified reliably.

According to yet another aspect of the present invention, a recordedinformation identification apparatus of an optical recording mediumrecorded with information on a substrate is provided. The opticalrecording medium includes a region in which the presence of pits havingat least two different depths formed on the substrate indicatesidentification information that is unique to the optical recordingmedium. The recorded information identification apparatus includes acircuit detecting a polarity of a tangential push-pull signal obtainedfrom the pits, the polarity differing according to the depth of a pit,and a circuit identifying the unique identification information based onthe detected polarity.

In an optical recording medium in which the presence of pits ofdifferent depths indicates identification information that is unique tothe optical recording medium of the present invention, the opticalrecording medium is identified based on the polarity of the tangentialpush-pull signal obtained from the pits. Therefore, the opticalrecording medium can be identified reliably.

According to yet a still further aspect of the present invention, anoptical recording medium that can have information recorded on asubstrate includes a first region having first information recorded atleast in a depth direction of a plane direction and depth direction ofthe substrate, and a second region than can have second informationrecorded in the plane direction of the substrate.

According to the present invention, more information can be recorded inthe first region since the recording density can be increased in thefirst region where information is recorded in the depth direction ascompared with a convention optical recording medium.

Since the first information in the first region is recorded in the depthdirection, copying to another recordable medium that records informationin the plane direction can be prevented.

According to an additional aspect of the present invention, areproduction method of an optical recording medium that can haveinformation recorded on a substrate is provided. The optical recordingin medium includes a first region having first information recorded atleast in a depth direction of the substrate by pits of at least twodifferent depths formed on the substrate, and a second region that canhave second information recorded in a plane direction of the substrateby at least one of the presence/absence, the length, the width and theposition of a mark formed on the substrate. The reproduction method ofan optical recording medium includes the steps of reproducing the firstinformation in the first region based on a polarity of a tangentialpush-pull signal obtained from the pits, the polarity differingaccording to the depth of a pit, and reproducing the second informationin the second region based on a signal representing a quantity ofreflected light obtained from the mark.

Since the first information is reproduced based on a tangentialpush-pull signal in the present invention, multivalued information cannow be reproduced that was not possible by the conventional reproductionmethod that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light from a mark in the second region, a conventionalreproduction circuit can be used for the reproduction circuit of thisregion. Accordingly, the cost of the reproduction apparatus can bereduced.

According to another aspect of the present invention, a reproductionmethod of an optical recording medium that can have information recordedon a substrate is provided. The optical recording medium includes afirst region having first information recorded at least in a depthdirection of the substrate by pits of at least two different depthsformed on the substrate, and a second region that can have secondinformation recorded in a plane direction of the substrate by at leastone of the presence/absence, the length, the width and the position of amark formed on the substrate. The reproduction method of an opticalrecording medium includes the steps of reproducing the first informationin the first region based on a signal representing a quantity ofreflected light obtained from the pit and a polarity of a tangentialpush-pull signal obtained from the pits, the polarity differingaccording to the depth of a pit, and reproducing the second informationin the second region based on the signal representing the quantity ofreflected light obtained from a mark.

Since the first information is reproduced based on a signal representingthe quantity of reflected light obtained from a pit and a tangentialpush-pull signal in the present invention, multivalued information cannow be reproduced that was not possible by the conventional reproductionmethod that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light from a mark in the second region, a conventionalreproduction circuit can be used for the reproduction circuit of thisregion. Accordingly, the cost of the reproduction apparatus can bereduced.

According to a further aspect of the present invention, a reproductionapparatus of an optical recording medium that can have informationrecorded on a substrate is provided. The optical recording mediumincludes a first region having first information recorded at least in adepth direction of the substrate by pits of at least two differentdepths formed on the substrate, and a second region that can have secondinformation recorded in a plane direction of the substrate by at leastone of the absence/presence, the length, the width and the position of amark formed on the substrate. The reproduction apparatus of the opticalrecording medium includes a circuit reproducing the first information inthe first region based on a polarity of a tangential push-pull signalobtained from the pits, the polarity differing according to the depth ofa pit, and a circuit reproducing the second information in the secondregion based on a signal representing the quantity of reflected lightobtained from a mark.

Since the first information is reproduced based on a tangentialpush-pull signal in the present invention, multivalued information cannow be reproduced that was not possible by the conventional reproductionapparatus that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light in the second region, a conventional reproductioncircuit can be used for the reproduction circuit of this region.Accordingly, the cost of the reproduction apparatus can be reduced.

According to still another aspect of the present invention, areproduction apparatus of an optical recording medium that can haveinformation recorded on a substrate is provided. The optical recordingmedium includes a first legion having first information recorded atleast in a depth direction of the substrate by pits of at least twodifferent depths formed on the substrate, and a second region that canhave second information recorded in a plane direction of the substrateby at least one of the presence/absence, the length, the width and theposition of a mark formed on the substrate. The reproduction apparatusof the optical recording medium includes a circuit reproducing the firstinformation in the first region based on a signal representing aquantity of reflected light obtained from the pit and a polarity of atangential push-pull signal obtained from the pits, the polaritydiffering according to the depth of a pit, and a circuit reproducing thesecond information in the second region based on the signal representingthe quantity of reflected light obtained from a mark.

Since the first information is reproduced based on a signal representingthe quantity of reflected light from a pit and a tangential push-pullsignal in the present invention, multivalued information can now bereproduced that was not possible by the conventional reproductionapparatus that reproduces binary information based on only a signalrepresenting the quantity of reflected light. Also, since the secondinformation is reproduced based on a signal representing the quantity ofreflected light in the second region, a conventional reproductioncircuit can be used for the reproduction circuit of this region.Accordingly, the cost of the reproduction apparatus can be reduced.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D schematically show the relationship between the structure ofan optical disk and signals obtained therefrom according to a firstembodiment of the present invention.

FIG. 2 is a block diagram representing a circuit configuration of themain part of an optical disk reproduction apparatus according to thefirst embodiment of the present invention.

FIG. 3 is a timing chart of the operation of the optical diskreproduction apparatus according to the first embodiment of FIG. 2.

FIG. 4 is a block diagram representing a circuit configuration of themain part of an optical disk reproduction apparatus according to asecond embodiment of the present invention.

FIGS. 5A-5D schematically show the relationship between the structure ofan optical disk and signals obtained therefrom according to a thirdembodiment of the present invention.

FIG. 6 schematically shows the arrangement of pits formed on aconventional ROM disk.

FIGS. 7A-7D schematically show the relationship between the structure ofa conventional optical disk of FIG. 6 and signals obtained therefrom.

FIGS. 8A and 8B schematically show the manner of a light beam spotrunning over a pit string and the manner of a detector receivingreflected light of the light beam spot.

FIG. 9 is a graph representing the relationship among the pit depth, TPPsignal amplitude and RF signal amplitude.

FIG. 10 is a timing chart representing the relationship among the pitdepth, RF signal and TPP signal.

FIGS. 11A-11D schematically show the relationship between the structureof an optical disk according to another conventional example and signalsobtained therefrom.

FIG. 12 is a schematic diagram showing a recordable disk of anotherconventional example in an unrecorded state.

FIGS. 13A-13D schematically show the relationship between a structure ofa conventional optical disk of FIG. 12 and signals obtained therefrom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As previously described in the section of the related art, binaryrecording is generally used that records information according to thepresence/absence, the length, the width, or the position in thesubstrate plane of pits, marks, and the like in an optical disk.However, information of larger capacity can be recorded if informationcan be provided additionally in the depth direction of the pit. Such atechnique is already proposed in a copending U.S. patent applicationSer. No. 09/606282 by the inventors of the present invention. Thetechnique is directed to additionally include information in the pitdepth taking advantage of the fact that the diffraction pattern causedby light interference generated in a pit that has a recessed andprotruded configuration differs depending upon the pit depth.

FIG. 9 is a graph representing the relationship of the depth of, forexample, pit 32 shown in FIG. 8A with respect to the amplitudes of an RFsignal and TPP signal obtained therefrom. The depth of pit 32 is plottedalong the horizontal axis with the wavelength X of the light beam usedfor reproduction as the reference. In the graph, n is the refractiveindex of the substrate of the optical disk. In the present example,experiments are carried out as to an optical disk including atransparent substrate having a thickness of 0.6 mm and a refractiveindex of 1.5 using a reproduction light beam of 650 nm in wavelength andan optical system having a numerical aperture (NA) of 0.65.

Referring to FIG. 9, the amplitude of an RF signal exhibits the maximumvalue when the pit depth is λ/4n (108 nm). The vertical axis at theright side in FIG. 9 is a normalized amplitude of the RF signal with 1as the maximum value. The amplitude of the TPP signal exhibits themaximum value when the pit depth is λ/8n (54 nm). The vertical axis atthe left side in FIG. 9 is a normalized amplitude of the TPP signal with1 as the maximum value. The TPP signal has its polarity inverted at theborder of pit length λ/4n. To clearly show this inversion, the sign ofthe TPP signal is set negative in the range of λ/4n (108 nm)<pitdepth<λ/2n (216 nm).

The polarity inversion of the TPP signal will be described hereinafterwith reference to FIGS. 9 and 10. It is assumed that pits 32 a and 32 bof FIG. 10 have a depth D1 (86 nm) and a depth D2 (130 nm),respectively. FIG. 10 represents the waveforms of the RF signal and TPPsignal obtained when a string of pits of such different depths isreproduced. In FIG. 10, the light beam moves from the left side to theright side. As shown in (a) of FIG. 10, the RF signal exhibits a smallerquantity of reflected light in the pit portion than in the non-pitportion in the pits of all depths. As to pit 32 a of depth D1, as shownin FIG. 10(b), the TPP signal exhibits a pulse in the positive direction(upwards in FIG. 10) at the leading edge of pit 32 a, and then exhibitsa pulse in the negative direction (downwards in FIG. 10) at the trailingedge of pit 32 a. As to pit 32 b of depth D2, the TPP signal exhibits apulse in the negative direction (downwards in FIG. 10) at the leadingedge of pit 32 b and then a pulse in the positive direction (upwards inFIG. 10) at the trailing edge of pit 32 b. This phenomenon is referredto as the inversion of the polarity of the TPP signal. In FIG. 9, thepolarity of the TPP signal obtained at pit 32 a of depth D1 isrepresented as positive and the opposite polarity of the TPP signal isrepresented as negative.

Embodiments of the present invention will be described hereinafter basedon this polarity inversion of a TPP signal according to theabove-described different pit depth.

First Embodiment

An optical recording medium and a reproduction method and apparatusthereof according to a first embodiment of the present invention will bedescribed hereinafter. FIGS. 1A and 1B schematically show a structure ofa pit string on a ROM disk as an example of an optical recording mediumin the first embodiment. FIGS. 1C and 1D represent the waveforms ofsignals obtained by reproducing information from the ROM disk.

More specifically, FIG. 1A schematically shows pit string 3 constitutedby two types of pits 2 a and 2 b, illustrated in a linear version fromthe inner circumference region to the outer circumference region of thedisk. FIG. 1B schematically shows the cross section of the disk,corresponding to pit string 3 of FIG. 1A. Referring to FIG. 1B, thelead-in region is formed of relatively shallow pits 2 a (depth D1) andrelatively deep pits 2 b (depth D2). The user region is formed of pits 2a of a constant depth (depth D1). FIG. 1C shows an RF signalrepresenting the quantity of reflected light obtained by reproducing pitstring 3 with a reproduction light beam. The quantity of reflected lightis smaller in the pit portion than in the non-pit portion. FIG. 1D showsa TPP signal obtained by reproducing pit string 3 with the reproductionlight beam. As shown in FIG. 1B, the lead-in region is formed of pits 2a and 2 b that have depth differing from each other. As describedpreviously in relation to FIGS. 9 and 10, the polarity of the obtainedTPP signal is inverted between relatively shallow pit 2 a and relativelydeep pit 2 b. More specifically, by forming the lead-in region with pits2 a and 2 b of two different depths in the first embodiment, informationcan be recorded in the depth direction of the disk substrate takingadvantage of the positive and negative values that are easily determinedas to the polarity of the TPP signal.

These two pit depths (D1, D2) are to be set so that RF signals of thesame amplitude and TPP signals of different polarity are obtained frompits 2 a and 2 b. More specifically, it will be understood from thegraph of FIG. 9 that the depths (D1, D2) are to be set so as to satisfy:λ/8n<D1<λ/4n and λ/4n<D2<3λ/8nwhere x is the wavelength of the reproduction light beam and n is therefractive index of the substrate.

The reproduction method and reproduction apparatus of informationrecorded in a lead-in region formed of two different types of pits 2 aand 2 bhaving-different depths and in a user region formed of one typeof pits 2 ahaving a constant depth will be described with reference toFIGS. 2 and 3.

FIG. 2 is a schematic block diagram showing a circuit configuration ofthe main part of a reproduction apparatus of the ROM disk shown inFIG. 1. FIG. 3 is a timing chart representing the operation of thereproduction apparatus of FIG. 2.

Description is based on the case where two types of pits 2 a and 2 barranged as shown in FIG. 3(a) are to be reproduced. It is assumed thatthe depths of the pit are D1, D2 and D1 from left to right in theexample of FIG. 3.

Referring to FIG. 2, the outputs obtained from respective regions A andB by directing reflected light 5 of reproduction beam spot from the diskto regions A and B of a detector 6 are both provided to a differentialamplifier 7 and an addition amplifier 8. Differential amplifier 7obtains the difference between the outputs of regions A and B ofdetector 6 to provide the difference as the TPP signal shown in FIG.3(c). Addition amplifier 8 obtains the total sum of the outputs ofregions A and B of detector 6 to provide the obtained value as the RFsignal of FIG. 3(b).

As to the RF signals indicating the quantity of reflected light of thelight beam (FIG. 3(b)), a correction process of the frequencycharacteristics and the like is carried out by an equalization circuit12 on an RF signal reproduced from a pit of a particularly short length.As shown in FIG. 3(d), the output of equalization circuit 12 isbinarized by a binarization circuit 13 and then provided to ademodulation circuit not shown to be subjected to the generaldemodulation process.

The TPP signal (FIG. 3(c)) is applied to both comparators 9 and 10.Comparator 9 compares the input TPP signal with a preset positivereference value. When the TPP signal is greater than the reference value(i.e., the sign of the TPP signal is positive and the absolute valuethereof is great), one pulse (+1) is generated as shown in FIG. 3(e) andprovided to one input of an adder-subtracter circuit 11. Similarly,comparator 10 compares the input TPP signal with a preset negativereference value. When the TPP signal is smaller than the reference value(i.e., the sign of the TPP signal is negative and the absolute valuethereof is large), one pulse (−1) is generated as shown in FIG. 3(f) andprovided to the other input of adder-subtracter circuit 11.

Adder-subtracter circuit 11 accumulates respective pulses fromcomparators 9 and 10 to output a signal indicating any one of the threestatuses of−1, 0, +1 obtained each time, as shown in FIG. 3(g), as anoutput signal of two bits. Similar to the RF signal, the output signalis provided to a demodulation circuit not shown to be subjected to thegeneral demodulation process.

More specifically, adder-subtracter circuit 11 operates (in the exampleof FIG. 3, adding operation including the polarity thereof is carriedout) on the pair of pulse strings ((e) and (f) in FIG. 3) obtained bybinarizing TPP signals by comparators 9 and 10. Based on the operationresult, the two statuses of −1 or +1 can be restored according to thepit depths in the pit portion (more specifically, the generationsequence of positive and negative pulses based on the TPP signal), andthe one status of 0 can be restored in the non-pit portion. Therefore,information of a total of three values can be recorded and reproduceddepending upon the absence/presence and the depth of the pit. As aresult, the recording density of information on an optical recordingmedium can be improved significantly as compared with the conventionalso-called binary recording.

In the user region of the disk, a reproducing operation similar to thatof the conventional binary recorded information is to be carried outsince all the pits have the same depth (D1). Referring to FIG. 3(c), inthe pit of depth D1, a positive TPP signal and a negative TPP signal aregenerated when the beam spot is located at the leading edge and trailingedge of the pit, respectively. By adding the pulses, including thesigns, of (e) and (f) of FIG. 3 that are obtained by binarizing thesepositive and negative TPP signals using adder-subtracter circuit 11, asignal of the two status of +1 at the pit portion and 0 at the non-pitportion can be obtained. Therefore, in the reproduction method andreproduction apparatus of the first embodiment of the present invention,the region having the main information recorded according to pits of thesame depth, i.e. the user region, can have binarization informationrestored and reproduced. The region having another information recordedaccording to pits of different depths, i.e. the lead-in region, can havethree-valued information restored and reproduced. The same reproductionmethod can be used for either region.

As to the region having the main information recorded according to pitsof the same depth, i.e. as to the user region, the binarizationinformation may be reproduced based on only a reproduced RF signal as inthe conventional case. In this case, a conventional circuit can be usedfor the reproduction circuit of the main information. As a result, thecost of the reproduction apparatus can be reduced.

Thus, in the lead-in region of the optical recording medium according tothe first embodiment of the present invention, information is recordedat least in the depth direction, or in the depth direction in additionto the plane direction of the substrate (conventional binary recording).Therefore, more information can be recorded in the lead-in region thanin the conventional ROM disk that has information recorded only in theplane direction. As a result, a usable region can be preserved orexpanded even if the amount of information recorded in the lead-inregion is increased.

Furthermore, copyright protection can be effected by recordinginformation in the depth direction in the lead-in region. This will bedescribed in detail hereinafter.

As described in relation to the conventional example of FIG. 13, thepolarity of the TPP signal obtained from the user region of a recordabledisk is identical for all marks 55 as shown in FIG. 13D since marks 55all have the same depth in the user region. Therefore, the informationrecorded in the depth direction (ternary recording) by pits 2 a and 2 bof different depths among the information in the lead-in region of theROM disk recorded as shown in FIG. 1B will by no means be transferred tothe user region (only binary recording possible) of the recordable disk.In other words, information in the lead-in region of the optical disk ofthe first embodiment will never be copied into another recordable disk.

By scrambling or encrypting the information in the user region in theoptical disk of the first embodiment and recording the cancel keythereof in the lead-in region using the depth direction, the cancel keyrecorded in the lead-in region will by no means be copied into anotherrecordable disk even if the information in the user region is copiedinto another recordable disk. This means that the information in the ROMdisk according to the first embodiment of the present inventionsubstantially cannot be copied.

It is to be noted that information unique to the disk such as diskidentification (ID) information other than the cancel key may besimilarly recorded in the depth direction of the lead-in region. By suchrecording, undesirable copying of these information to a recordable diskcan be inhibited completely. In other words, illegal copy of a disk thatincludes copyrighted contents can be prevented.

Although the above-described first embodiment corresponds to the casewhere information is recorded at least in the depth direction of thelead-in region, it will be understood that the region where recording isto be effected in the depth direction is not limited to a lead-inregion, and can be effected on any region of the optical disk. Morespecifically, it is impossible to copy information from a region wherethe information is recorded in the depth direction to another recordabledisk. Such a region can be identified as a unique region (for example,the above-described lead-in region) in the optical disk.

The above-described embodiment is directed to a transparent substratehaving a thickness of 0.6 mm and a refractive index of 1.5 using a lightbeam having a wavelength of 650 nm and an optical system having an NA of0.6. However, it is apparent that the above-described effect is notlimited to the type of the used optical system, substrate or the like.Furthermore, the values of the pit depths are not limited to those shownin the above embodiment. According to the principle of the presentinvention, it is clear that depths are to be selected so that thepolarity of the TPP signal differs for respective pits. Since arecordable disk does not have a recording dimension in the depthdirection, copying information from an optical disk having a regionrecorded with information in the depth direction according to theabove-described embodiment to a recordable disk can be inhibited. It isalso apparent that the specific method therefor is not limited to thatdescribed above.

Second Embodiment

Referring to FIG. 4, an identify circuit of recorded information in areproduction apparatus of an optical recording medium according to asecond embodiment of the present invention will be described withreference to FIG. 4. More particularly, FIG. 4 is a block diagramshowing the circuit configuration that allows detection of the presenceof pits from which a TPP signal of different polarity can be obtained onthe optical disk.

Similar to the reproduction apparatus of the first embodiment shown inFIG. 2, the outputs from regions A and B of detector 6 are provided todifferential amplifier 7 and addition amplifier 8. Similar to the firstembodiment of FIG. 2, the TPP signal which is the output of differentialamplifier 7 is applied to comparators 9 and 10. The TPP signalsbinarized by respective comparators 9 and 10 are applied to a markerdetection circuit 15. The RF signal which is the output of additionamplifier 8 is provided to comparator 14 to be compared with apredetermined reference value. The RF signal binarized by comparator 14is also applied to marker detection circuit 15.

Marker detection circuit 15 determines whether there is a pit thatcauses the polarity of the TPP signal to be inverted for respective pitsbased on the binarization signals (FIG. 3(e) and (f)) output fromcomparators 9 and 10 and the binarization signal (FIG. 3(d)) output fromcomparator 14.

By the output of marker detection circuit 15, determination is made asto whether the optical recording medium subjected to reproduction is adisk having a region in which information is recorded in the depthdirection. According to the second embodiment of the present invention,the presence of pits of different depths can be used as the so-calledidentification marker (ID) to identify that optical recording medium.

Third Embodiment

A recordable disk as an example of an optical recording medium accordingto a third embodiment of the present invention will be described herewith reference to FIGS. 5A-5D. FIGS. 5A and 5B schematically show thestructure of a mark string and pit string on a recordable disk accordingto the third embodiment. FIGS. 5C and 5D represent the waveforms ofsignals obtained by reproducing the information recorded on the disk.

In general, mark 25 is written in either or both of the groove and land.The third embodiment of FIG. 5 corresponds to the example where marks 25are written in groove 24.

More specifically, FIG. 5A schematically shows mark strings 26constituted by marks 25 formed in groove 24 and a pit string 23constituted by pits 22 a and 22 b arranged between these mark strings,illustrated in a linear version from the inner circumference region tothe outer circumference region of the disk. FIG. 5B schematically showsthe cross section of the disk corresponding to mark string 26 and pitstring 23 of FIG. 5A. Pit string 23 formed in the lead-in region isconstituted by relatively shallow pits 22 a (depth D1) and relativelydeep pits 22 b (depth D2). More specifically, the third embodiment isdifferent from the conventional recordable disk shown in FIG. 13 in thatthe pits forming pit string 23 are formed of two types of pits, i.e.relatively shallow pits 22 a and relatively deep pits 22 b.

FIG. 5C shows an RF signal representing the quantity of reflected lightobtained by reproducing mark string 26 and pit string 23 with areproduction light beam. It is noted that the quantity of reflectedlight of the mark portion and the pit portion is smaller than thequantity of reflected light of the non-mark portion and non-pit portion.

FIG. 5D represents a TPP signal obtained by reproducing mark string 26and pit string 23 with a reproduction light beam. The polarity of TPPsignals obtained from mark 25 and relatively shallow pit 22 a areidentical. Only the polarity of a TPP signal obtained from relativelydeep pit 22 b is inverted. More specifically, by forming the lead-inregion with pits 22 a and 22 b of two different depths, information canbe recorded in the depth direction of a disk substrate taking advantageof the positive and negative values, that is, the polarity of the TPPsignal, that are easy to determine.

These two different pit depths D1 and D2 are to be set so that RFsignals of the same amplitude and TPP signals of different polarity areobtained from pits 22 a and 22 b. More specifically, similar to thefirst embodiment, depths D1 and D2 are to be set so as to satisfy:λ/8n<D1<λ/4n and λ/4n<D2<3λ/8nwhere X is the wavelength of the light beam and n is the refractiveindex of the substrate.

As to a reproduction method and reproduction apparatus of a signal frompit string 23 formed of pits 22 a and 22 b of two different types ofdepth and mark string 26 formed of marks 25 are substantially identicalto those of the optical disk of the first embodiment described withreference to FIGS. 2 and 3. Therefore, description will not be repeatedfor the common elements.

More specifically, similar to the reproduction apparatus of the firstembodiment, the reproduction apparatus of the third embodiment includesan adder-subtracter circuit 11 that applies an operation on a pair ofpulse signals (adding operation including polarity) obtained bybinarizing respective TPP signals by comparators 9 and 10. Based on theresults of the operation, the two statuses of −1 or +1 can be restoredaccording to the pit depth in the pit portion. In the non-pit portion,one status of 0 can be restored. Therefore, information of the total ofthree values can be recorded and reproduced depending upon theabsence/presence and depth of the pit. As a result, the recordingdensity of information on the optical recording medium can be increasedsignificantly than by the conventional so-called binary recording.

According to the reproduction method and reproduction apparatus of thethird embodiment, the RF signal and TPP signal can be shared in order toreproduce a signal from the mark portion. More specifically, referringto FIG. 5D, a positive TPP signal and a negative TPP signal are obtainedwhen the beam spot is located at the leading edge and trailing edge,respectively, for mark 25. Therefore, similar to the reproductionapparatus of the first embodiment shown in FIG. 2, by accumulating pulsesignals (FIG. 3(e), (f)) obtained by binarizing the TPP signal atadder-subtracter circuit 11, the two statuses of +1 at the mark portionand 0 at the non-mark portion can be achieved. More specifically,binarization information for the mark portion and ternary informationfor the pit portions of different depths can be respectively restoredand reproduced in the present reproduction method or reproductionapparatus of recorded information. The same reproduction method can beapplied for either region.

In the third embodiment of FIG. 5, the region where the main informationis recorded with pits of the same depth, i.e., the user region, can havebinarization information reproduced from only an RF signal as in theconventional case. In this case, the conventional circuit can be usedfor the reproduction circuit of the main information. As a result, thecost of the reproduction apparatus can be reduced.

Thus, since the lead-in region of the recordable optical disk of thethird embodiment of the present invention can have information recordedat least in the depth direction, or in the depth direction in additionto the substrate plane direction (conventional binary recording), moreinformation can be recorded in the lead-in region than in theconventional recordable disk that records information only in the planedirection. As a result, a usable region can be preserved or enlargedeven if the amount of information to be recorded in the lead-in regionincreases.

By recording information in the depth direction in the lead-in region.in the present third embodiment shown in FIG. 5, copyright protectioncan be effected. This will be described in detail hereinafter.

Since the depth of the recording marks in the recordable region (userregion) of the recordable disk of FIG. 5 is constant, the polarity ofthe TPP signal is identical for all the marks as shown in FIG. 5D.Therefore, the information recorded in the depth direction by pits 22 aand 22 b of different depth of the recorded information in the lead-inregion of the recordable disk in FIG. 5B will by no means be transferredto the user region of the recordable disk. In other words, informationin the lead-in region of the optical disk of the third embodiment cannever be copied to another recordable disk.

By scrambling or encrypting the information in the user region in theoptical disk of the third embodiment and recording the cancel key in thelead-in region using the depth direction as described above, the cancelkey recorded at the lead-in region will never be copied even if theinformation in the user region is copied into the another recordabledisk. Therefore, copying information in the recordable disk by the thirdembodiment is inhibited.

It is to be noted that information unique to the disk such as diskidentification (ID) information other than the cancel key may besimilarly recorded in the depth direction of the lead-in region. By suchrecording, undesirable copying of these information to anotherrecordable disk can be inhibited completely. In other words, illegalcopying of a disk that includes copyrighted contents can be prevented.

The above-described embodiment is directed to a transparent substratehaving a thickness of 0.6 mm and a refractive index of 1.5 using a lightbeam having a wavelength of 650 nm and an optical system having an NA of0.6. However, it is apparent that the above-described effect is notlimited to the type of the used optical system, substrate or the like.Furthermore, the values of the pit depths are not limited to those shownin the above embodiment. According to the principle of the presentinvention, it is clear that depths are to be selected so that thepolarity of the TPP signal differs for respective pits. Since arecordable region (user region) of the above-described recordable diskis absent of a recording dimension in the depth direction, copyinginformation from an optical disk having a region recorded withinformation in the depth direction according to the above-describedembodiment to a recordable disk can be inhibited. It is also apparentthat the specific method therefor is not limited to that describedabove.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. (canceled)
 14. A reproduction method of anoptical recording medium recorded with information on a substrate, saidoptical recording medium including a first region having firstinformation recorded at least in a depth direction of said substrate bypits of at least two different depths formed on said substrate, and asecond region having second information recorded in a plane direction ofsaid substrate by at least one of the presence/absence, the length, thewidth and the position of a pit formed on said substrate, saidreproduction method comprising the steps of: reproducing said firstinformation in said first region based on a polarity of a tangentialpush-pull signal obtained from said pits, said polarity differingaccording to the depth of a pit, and reproducing said second informationin said second region based on a signal representing a quantity ofreflected light obtained from said pit.
 15. A reproduction method of anoptical recording medium recorded with information on a substrate, saidoptical recording medium including a first region having firstinformation recorded at least in a depth direction of said substrate bypits of at least two different depths formed on said substrate, and asecond region having second information recorded in a plane direction ofsaid substrate by at least one of the absence/presence, the length, thewidth and the position of a pit formed on said substrate, saidreproduction method comprising the steps of: reproducing said firstinformation in said first region based on a signal representing aquantity of reflected light obtained from said pit and a polarity of atangential push-pull signal obtained from said pits, said polaritydiffering according to the depth of a pit, and reproducing said secondinformation in said second region based on said signal representing thequantity of reflected light obtained from said pit.
 16. A reproductionapparatus of an optical recording medium recorded with information on asubstrate, said optical recording medium including a first region havingfirst information recorded at least in a depth direction of saidsubstrate by pits of at least two different depths formed on saidsubstrate, and a second region having second information recorded in aplane direction of said substrate by at least one of thepresence/absence, the length, the width and the position of a pit formedon said substrate, said reproduction apparatus comprising: a circuitreproducing said first information in said first region based on apolarity of a tangential push-pull signal obtained from said pits, saidpolarity differing according to the depth of a pit, and a circuitreproducing said second information in said second region based on asignal representing the quantity of reflected light obtained from saidpit.
 17. A reproduction apparatus of an optical recording mediumrecorded with information on a substrate, said optical recording mediumincluding a first region having first information recorded at least in adepth direction of said substrate by pits of at least two differentdepths formed on said substrate, and a second region having secondinformation recorded in a plane direction of said substrate by at leastone of the presence/absence, the length, the width and the position of apit formed on said substrate, said reproduction apparatus comprising: acircuit reproducing said first information in said first region based ona signal representing a quantity of reflected light obtained from saidpit, and a polarity of a tangential push-pull signal obtained from saidpits, said polarity differing according to the depth of a pit, and acircuit reproducing said second information in said second region basedon said signal representing the quantity of reflected light obtainedfrom said pit.
 18. A recorded information identification method of anoptical recording medium recorded with information on a substrate, saidoptical recording medium including a region in which the presence ofpits having at least two different depths formed on said substrateindicates identification information that is unique to said opticalrecording medium, said identification method comprising the steps of:detecting a polarity of a tangential push-pull signal obtained from saidpits, said polarity differing according to the depth of a pit in saidregion, and identifying said unique identification information based onsaid detected polarity.
 19. A recorded information identificationapparatus of an optical recording medium recorded with information on asubstrate, said optical recording medium including a region in which thepresence of pits having at least two different depths formed on saidsubstrate indicates identification information that is unique to saidoptical recording medium, said recognition apparatus comprising: acircuit detecting a polarity of a tangential push-pull signal obtainedfrom said pits, said polarity differing according to the depth of a pitin said region, and a circuit identifying said unique identificationinformation based on said detected polarity.
 20. An optical recordingmedium that can have information recorded on a substrate, comprising: afirst region having first information recorded at least in a depthdirection of a plane direction and depth direction of said substrate,and a second region that can have second information recorded in theplane direction of said substrate.
 21. The optical recording mediumaccording to claim 20, wherein said first information is recorded insaid first region at least in said depth direction by at least a depthof a pit of the absence/presence, the length, the width, the positionand the depth of the pit formed on said substrate, and said secondinformation is recorded in said second region in said plane direction byat least one of the presence/absence, the length, the width, and theposition of a mark formed on said substrate.
 22. The optical recordingmedium according to claim 21, wherein said first region has said firstinformation recorded in said depth direction by said pits having atleast two different depths.
 23. The optical recording medium accordingto claim 22, wherein a tangential push-pull signal differing in polarityaccording to the depth of a pit is obtained from said pits having atleast two different depths when reproducing said first information fromsaid first region.
 24. The optical recording medium according to claim22, wherein said two different depths of said pits are set so as tosatisfy:λ/8n<D1<λ/4n and λ/4n<D2<3λ/8n where D1 and D2 are the respective twodifferent depths, k is a wavelength of light used in reproducing saidfirst information, and n is a refractive index of said substrate. 25.The optical recording medium according to claim 20, wherein said firstinformation recorded in said first region includes additionalinformation required for reproduction of said optical recording medium.26. The optical recording medium according to claim 25, wherein saidadditional information includes information inhibited of being copiedinto another recording medium.
 27. The optical recording mediumaccording to claim 25, wherein said second information that can berecorded in said second region includes main information.
 28. Theoptical recording medium according to claim 27, wherein said additionalinformation includes information required for reproduction of said maininformation.
 29. The optical recording medium according to claim 28wherein said additional information includes key information to cancelscrambling or encryption of said main information.
 30. The opticalrecording medium according to claim 25, wherein said additionalinformation includes information unique to said optical recording mediumitself.
 31. The optical recording medium according to claim 30, whereinsaid additional information includes information to identify saidoptical recording medium.
 32. A reproduction method of an opticalrecording medium that can have information recorded on a substrate, saidoptical recording medium including a first region having firstinformation recorded at least in a depth direction of said substrate bypits of at least two different depths formed on said substrate, and asecond region that can have second information recorded in a planedirection of said substrate by at least one of the presence/absence, thelength, the width and the position of a mark formed on said substrate,said reproduction method comprising the steps of: reproducing said firstinformation in said first region based on a polarity of a tangentialpush-pull signal obtained from said pits, said polarity differingaccording to the depth of a pit, and reproducing said second informationin said second region based on a signal representing a quantity ofreflected light obtained from said mark.
 33. A reproduction method of anoptical recording medium that can have information recorded on asubstrate, said optical recording medium including a first region havingfirst information recorded at least in a depth direction of saidsubstrate by pits of at least two different depths formed on saidsubstrate, and a second region that can have second information recordedin a plane direction of said substrate by at least one of theabsence/presence, the length, the width and the position of a markformed on said substrate, said reproduction method comprising the stepsof: reproducing said first information in said first region based on asignal representing a quantity of reflected light obtained from said pitand a polarity of a tangential push-pull signal obtained from said pits,said polarity differing according to the depth of a pit, and reproducingsaid second information in said second region based on said signalrepresenting the quantity of reflected light obtained from said mark.34. A reproduction apparatus of an optical recording medium that canhave information recorded on a substrate, said optical recording mediumincluding a first region having first information recorded at least in adepth direction of said substrate by pits of at least two differentdepths formed on said substrate, and a second region that can havesecond information recorded in a plane direction of said substrate by atleast one of the presence/absence, the length, the width and theposition of a mark formed on said substrate, said reproduction apparatuscomprising: a circuit reproducing said first information in said firstregion based on a polarity of a tangential push-pull signal obtainedfrom said pits, said polarity differing according to the depth of a pit,and a circuit reproducing said second information in said second regionbased on a signal representing the quantity of reflected light obtainedfrom said mark.
 35. A reproduction apparatus of an optical recordingmedium that can have information recorded on a substrate, said opticalrecording medium including a first region having first informationrecorded at least in a depth direction of said substrate by pits of atleast two different depths formed on said substrate, and a second regionthat can have second information recorded in a plane direction of saidsubstrate by at least one of the presence/absence, the length, the widthand the position of a mark formed on said substrate, said reproductionapparatus comprising: a circuit reproducing said first information insaid first region based on a signal representing a quantity of reflectedlight obtained from said pit and a polarity of a tangential push-pullsignal obtained from said pits, said polarity differing according to thedepth of a pit and a circuit reproducing said second information in saidsecond region based on said signal representing the quantity ofreflected light obtained from said mark.